This invention relates to a multilayer printed circuit board, a process for producing the same and a thermosetting resin composition usuable as insulating material for such a multilayer printed circuit board, etc. More particularly, the present invention relates to a multilayer printed circuit board having a high density, a high signal transmission speed and flame retardance, and a process for producing the same.
Recently, large-sized electronic computers are required to have a higher density, and high speed operation. Thus, multilayer printed circuit boards used therefor are also required to show such properties with severe demands. Generally speaking, the operation speed of an electronic computer is greatly influenced by the signal transmission speed of circuits in multilayer printed circuit boards. In order to improve the signal transmission speed of circuits, it is necessary to develop flame retardant resin materials excellent in adhesiveness to conductor circuit layers (mainly made of copper).
Fluorine-containing materials heretofore used such as polytetrafluoroethylene (PTFE) are thermoplastic resins, so that there were problems in poor dimensional stability and poor through hole reliability when used in multilayer printed circuit boards. Further, since there were no suitable solvents, adhesion of laminated layers should have been conducted by a melt pressure bonding method. But since the melting temperature was so high (e.g. 250.degree. to 350.degree. C.) that there were problems in that the workability was poor and the handling was difficult compared with epoxy resins and the like.
On the other hand, there is developed a resin material comprising 1,2-polybutadiene having double bonds at side chains and a cross-linking type fire retardant of bifunctional monomer (Japanese Patent Unexamined Publication No. 55-1264751). But when a low molecular weight polymer is used considering impregnating properties into fibrous substrates, the resulting prepreg is poor in cutting processing and storage due to high adhesiveness of the prepreg, and also influences workability at the time of bonding of laminated layers.
A material for producing a multilayer printed circuit board containing a cyanate compound is disclosed in U.S. Pat. No. 4,559,394.